A Photon Switch Based on the Quantum Nonlocality

We present a scheme to realize a photon switch for controlling the state of the field in a cavity between a coherent state and a Schrödinger cat state. In the scheme, an atom crosses two cavities continually. The atom is resonant with the first cavity mode, and off-resonant with the second cavity mode. The detection of the atomic state leaves the two cavity modes in an entangled state. We can determine whether the second cavity field is in a coherent state or in a Schrödinger cat state via the detection of the photon in the first cavity.